1. Field of the Invention
The present invention relates to a method and apparatus for contactless acquisition of data for the locally resolved determination of the instantaneous density and/or temperature ("density distribution", "temperature distribution") of a molecular gas in a measurement volume which can have a relatively large area and a relatively small thickness by laser-induced fluorescence (LIF).
2. Description of the Prior Art
It is known from the journal CHEMICAL PHYSICS LETTERS Volume 114, No. 5, 6, Mar. 15, 1985, p. 451-455 to excite selectively individual rotational vibrational states of molecular oxygen at pressures up to about 0.4 MPa by laser radiation and to measure the resulting laser-induced fluorescence (LIF).
The use of the known methods operating with laser-induced fluorescence (LIF) for determining densities and temperatures in a gas mixture is problematical at relatively high pressures because the fluorescence intensity is governed substantially by conditions of the laser-excited molecules with the surrounding gas, the so-called "quenching". The quenching depends via the collision parameters, in particular the collision frequency, on the instantaneous gas composition (the partial densities n.sub.i of the components of the gas mixture) and on the temperature LIF is therefore not suitable for example for exact investigations of combustion processes in internal-combustion engines and the like because both the gas composition and the temperature in the combustion chamber are parameters which vary greatly depending on the location and time and the quenching is therefore also a complicated function dependent on location and time and basically not known.